Gas heaters of the type here under consideration have a plurality of individual heating elements which are often in the form of ceramic plaques. A gaseous fuel and air mixture burns on the surface of the plaques, which in turn radiate the heat. The gaseous fuel supply may be either natural gas or propane gas.
One form of prior art heater is the VANGUARD heater manufactured by DESA International, Inc., 2701 Industrial Drive, Bowling Green, Ky. 42102, the assignee of the present application. A schematic representation of this heater is shown in FIG. 1A.
Referring now to FIG. 1A, a gas supply, either natural gas or propane, is delivered to a main regulator 10. The gas then passes through a conduit 12 to an infrared burner control valve 14, which is operated by a selection knob 15. The knob is movable between "off," "pilot," "low," "thermostat" and "high" positions.
A thermostat switch 16, which is energized from a power supply 18 (normally 120 volts, 60 Hertz), operates a solenoid valve 20 through a circuit board assembly 22.
The VANGUARD heater includes five infrared burners or plaques labeled A through E. Plaques C and D receive their gas supply through a conduit 24 in communication with the control valve 14; these two plaques are on all the time the heater is heating. When the selection knob 15 is in the "off" or "pilot" position, no burners are active. When selection knob 15 is in the "thermostat" position, the flow of gas supplied to plaques A, B and E through conduit 19 is controlled by the solenoid valve 20, which depends on the setting of the thermostat switch 16. When the selection knob 15 is in the "high" position, a conduit 17 bypasses the solenoid valve 20 and supplies fuel to plaques A, B and E.
In the thermostatic mode of operation, the knob 15 is moved to the "thermostat" position, and the thermostat switch 16 is rotated to a desired setting, anywhere between "high" and "low" positions. If more heat is required to achieve a temperature commensurate with the thermostat setting, combustion occurs on all five plaques. Once the thermostat is satisfied, the heater modulates to the two plaques C and D. When the room cools down, the thermostat again calls for heat and combustion occurs on all five plaques.
It is apparent that the VANGUARD heater is somewhat limited in that modulation can occur only between all plaques and two plaques. Furthermore, electricity is required of the solenoid 20 while in the thermostat mode. Thus, in the event of a power outage, the heater cannot operate in the "thermostat" mode, but can be operated only in either "low" or "high" positions. In the "low" mode, only burners C and D will operate. In the "high" position, all five plaques will operate.
Another form of heater is a TB model, gas-fire, infrared room heater, sold by Rinnai America Corporation, 1662 Forest Avenue, LaGrange, Ga. 30240. A schematic of that heater is shown in FIG. 1B.
The RINNAI heater works similar to the VANGUARD heater but with two plaques, A and B, instead of five. A fuel supply of either natural gas or propane gas is delivered to an infrared burner control valve and main regulator 30.
An infrared burner selection knob 32 is movable to positions "off," "pilot," "low" and "high." While in the "off" or "pilot" position, neither burner is active. While selection knob 32 is in the "low" position, the control valve 30 continuously fuels burner A through conduit 31. When the knob 32 is moved to "high," both burner A and B are active, but burner B is thermostatically controlled by electrical power.
A main switch 36 governs the power supply 38 (normally 120 volts and 60 Hertz) to the whole system. The power supply 38 energizes a thermostat switch 40, a warm air circulating blower 42 and a rectifier 44, which converts the alternating current to direct current for purposes of powering the solenoid 46.
In the thermostatic mode of operation, the knob 32 is moved to the "high" position and the thermostatic switch 40 is rotated to a desired temperature setting, anywhere between "high" and "low" positions. The thermostat switch 40 via rectifier 44 controls the solenoid valve 46 to regulate the flow of gas supplied to burner B through conduit 48. Gas is supplied to burner B when more heating is required to achieve a temperature commensurate with the setting of the thermostat switch 40. The gas to burner A is unregulated and continues flowing regardless of the setting on the thermostat switch 40.
The RINNAI heater has limitations similar to the VANGUARD heater. Modulation can only occur between 1 and 2 burners. Because the RINNAI heater is electrically powered, it is also affected by a power outage. In the event of a power outage, the heater would operate at only the "low" position; control of burner B by thermostat switch 40 would not be possible.
Furthermore, when available, electricity provides a possible hazard. The electrical source provides a potential ignition source in the event that damage to the heater or a malfunction causes a gas leak.